Evaluation of Intrinsic Biodegradation and

Amendments to Support Enhanced Monitored Natural

Recovery of SedimentsTom Krug and David Himmelheber, Geosyntec Consultants

Jeff Roberts, SiREM Laboratories

Outline

Sediment Remedies

Monitored Natural Recovery (MNR) Processes

Enhanced MNR (EMNR) Processes

Treatability Testing to Understand EMNR

Sorption / Sequestration

Biodegradation

Sediment Remedies

Dredging / Removal

Isolation Capping

MNR

EMNR Thin Layer Capping

In Situ Treatment

Active Capping

Combinations of all of the above

Monitored Natural Recovery (MNR)

Natural processes that reduce concentrations,

toxicity, bioavailability or exposure over time

Key mechanisms are: degradation or conversion to less toxic form,

sorption or sequestration,

reduction of exposure through deposition of new clean

sediment, or

reduction of concentrations through dispersion or dilution

EMNR Processes

Physical Thin layer cap

Chemical Sorption of PAH, PCB and mercury

Sequestration/precipitation of mercury

Biological Anaerobic reductive dechlorination of

chlorinated compounds (CB, PCBs)

Aerobic biodegradation (PAH, BTEX)

Understanding how natural processes (MNR) act to

reduce risks and using this knowledge to: predict future concentrations and risks

understand how to enhance these processes (EMNR)

Enhancing these processes may involve

amendments to: sorb or sequester target compounds

address nutrient or microbial limitations

Implementing EMNR

biodegradation of chlorinated organics

biodegradation of BTEX and PAH

sorption of PAHs with activated carbon

sorption / sequestration of PCBs and Hg & MeHg with activated carbon and other sorbents

Site Water

Site Sediment

Sorption / Sequestration Processes

Hydrophobic Organic Compounds (HOCs) (such as PAH & PCB) and metals can be sorbed onto many different forms of carbon in sediment

Porewater concentrations of HOCs in un-amended sediment will be a function of the fraction of organic carbon (foc)

Amendment with activated carbon or similar materials can reduce porewater concentrations, mobility, bioavailability, and risk

Direct addition of bulk activated carbon granular activated carbon (GAC) powdered activated Carbon (PAC)

Activated carbon incorporated into products such as Sedimite, AquaBlok or AquaGate

Biochar (less expensive form of carbon)

Case Study of Treatability Testing for PAH in Sediment

Evaluation of remedial options for PAH impacted sediments adjacent to historical MGP site

Treatability testing conducted to evaluate natural and enhanced processes for PAHs:

Anaerobic + aerobic biodegradation

Sequestration via activated carbon addition

Test results indicated that:

Intrinsic aerobic biodegradation of PAHs in Site sediment was possible

Activated carbon addition (1%) reduced porewater PAH levels to non-detect

Test results support use of MNR and use of carbon amendment if MNR will not achieve objectives in necessary time frame

Case Study of Treatability Testing for PAH in Sediment

Amendment with activated carbon or other sorbents can reduce Hg and MeHg porewater concentrations through sorption

Research suggests other amendments can reduce Hg and MeHg – mechanisms may include co-precipitation and reduced bioavailability to Hg methylating bacteria

Treatability testing can demonstrate site specific impacts of different amendments

Biodegradation Processes

Biological Reductive Dechlorination

Chlorinated Solvents (PCE, TCE, TCA) Anaerobic reductive dechlorination process

Dehalococcoides (Dhc), Dehalobacter (Dhb), Dehalogenimonas (Dhg), Geobacter

Common practice for groundwater remediation

Chlorinated Benzenes (TCB, DCM, MCB) Same processes and bacteria as for chlorinated solvents

Polychlorinated Biphenyl (PCBs) Same processes and bacteria but complicated by 209

difference PCB congeners

Biodegradation of Chlorobenzenes (CB)

TCB DCB MCB benzene

C

CC

C

CC

Cl

H

Cl

H

H

HC

CC

C

CC

Cl

H

H

H

H

H

C

CC

C

CC H

H

H

H

H

HDCB MCB Benzene

Anaerobic

Aerobic

Microcosm Test Results for Chlorobenzenes

1,2-DCB

1,4-DCB 1,3-DCB

Benzene

MCB

Time (days)

Also biodegrade

under aerobic conditions

Stability of PCBs in industrial applications also makes them stable in the environment

Activated carbon and other sorbents can reduce bioavailability

Biological reductive dechlorination also demonstrated but seldom incorporated into sediment management plans

C

CC

C

CC

Cl

H

H

H

C

CC

C

CC

Cl

H

H Cl

ClCl

Specific pathways of anaerobic reductive dechlorination of

PCBs have been identified

Dehalococcoides (Dhc), and related Chloroflexi have been

identified in the processes

Field evidence from Hudson River and other sites

demonstrates that dechlorination is occurring Anaerobic processes produce mono-, di- and tri- Cl PCB

which are: More soluble in water & less bioaccumulative Lower toxicity More likely to biodegrade under aerobic conditions

Analysis of PCB homologs or congeners can identify the

extent to which reductive dechlorination has occurred: data can be used to understand the characteristics of PCBs

present and potential risks

predict what changes may happen in the future

Treatability testing can further demonstrate the site specific

potential for reductive dechlorination (intrinsic and

enhanced) and help: better predict what changes may happen in the future

assess the potential benefits of enhancing biodegradation

EMNR can be used to mitigate risks associated with impacted sediment but requires: understanding natural physical, chemical and

biological processes demonstrating through site specific lab and pilot

testing how these processes can be enhanced to provide greater or faster risk mitigation

implementing and monitoring

Questions